Dogs with D. immitis infection will be utilized as a source of parasites and cells to study the humoral and cellular requirements for killing of microfilariae. Lymphocyte blastogenesis in infected dogs to mitogens and related and unrelated antigens will be tested in vitro. Further examination of cellular immunity in O. volvulus infected persons will be made using purified microfilarial antigens. Mechanisms of complement activation by microfilariae will be examined.